Measuring — Point Micrometer

A "point micrometer" is a special measuring tool that measures the thickness of an uneven surface. Here, it is used to measure the thickness of the brake track:

     

While such measurement is useful, note that it does not measure the inside the box section, and that may be much thinner. In this case, the thinnest part in the box is about 0.35 mm, but the micrometer measures about 0.70 mm.

In addition the point micrometer cannot reach well in to corners very well. Here, it gets close, but hits the tube bed and cannot quite measure the thinnest part. Although it gets close, a rim with a flatter tube bed would make it harder for the micrometer to reach in to the corner.

The point micrometer is also cumbersome to use because the tire and tube must be removed in order to measure rim wear. Since flat tires are often discovered while riding, this means fewer opportunities to measure with a point micrometer when tire and tube are off anyway.

Thus, the point micrometer is a good tool, but it would be better if makers provided a rim profile suitable for external measurement. Except in cases of uneven rim wear, that would probably give good accuracy without removing tire and tube, and would allow measurement of the region inside the box.